Hydrocarbon-soluble alkali metal compositions



Uted States PatCI tO 3,013,869 HYDROCARBON-SOLUBLE ALKALI METAL COMPOSITIONS Erik Kissa, Wilmington, DeL, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., :1 corporation of Delaware No Drawing. Filed Feb. 16, 1959, Ser. No. 793,263 3 Claims. (CI. 44-66) lines can be improved by the addition of such solvents as alcohol, such mixtures are not entirely satisfactory because of the large amount of alcohol which must be employed to produce even relatively low concentrations of the salt in the hydrocarbon fuel.

' It is an object of the present invention to pro-videcompositions of lithium salts of aliphatic branched chain carboxylic acids which are readily soluble in liquid hythereto of a. suitable lithium base.

adecanoic, 2,Z-dimethyloctadecanoic, campholic acid (1,-

l-carboxylic acid, l-methyl-2,5-endomethylene-cyclohex-- ane-l-carboxylic acid, 3-ethylpent-2-enoic, and 3-ethylpent-3-enoic acid. 1

Either the same acid used in making the lithium salt or a different acid of the class may be used to increase the solubility of the salt in hydrocarbon fuels. A difierent acid is preferred, since increased solubility is usually obtained. It is of course understood that mixtures of acids can be used to increase the solubility of a single salt or mixtures of salts.

The acid-salt compositions of the present invention may be prepared simply by mixing a lithium carboxylate and a carboxylic acid of the class defined. The components may be mechanically mixed, or fused by heating, or they may be brought together in a solvent. If the solvent is a low-boiling alcohol or benzene, it is readily removed from the acid-salt mixture and the mixture recovered by distilling otf the solvent. Alternately, the acid may be partially neutralized to the desired extent by the addition Similarly, the acidsalt composition may be prepared in a volatile liquid hydrocarbon, which hydrocarbon may or may not be redrocarbons, which compositions as such, or as'concenlithium salts of branched'chain carboxylic acids that can be dissolved in liquid hydrocarbons can be materially increased by incorporating therewith a hydrocarbonsoluble, branched chain carboxylic acid. The molar ratio of the acid to the lithium salt will ordinarily be within the range of from 10:1 to 0.5 :1. By this method it has been found that sufficient lithium salts can be put in solution in liquid hydrocarbons so as to provide at least about 0.0025 gram of lithium per liter of solution. The ratio of acid to salt can be decreased even below the 0.5 :1 Where relatively small additions of othersolvent such as alcohol are employed. The lithium salts of aliphatic branched chain carboxylic acids with which the present invention is involved are those containing from 4 to carbon atoms and which have at least one open chain'branch attached to one of the first six carbon atoms in the molecule. Since the branchings on the chain may join to form a cycloaliphatic ring, the term aliphatic branched chain? is meant to include cycloaliphatic and also the aliphaticcycloaliphatic types. 'These branched chain aliphatic carboxylic acids may also have aromatic rings attached to the carbon chains. The free acidsused as solubilizing agents are of the same class as those used in making the lithium salts. 1

Representative acids of this class from which the lithium salts may be derived and which as .free acids may be used as solubillizing agents for the lithiumsalts, are: isobutyric (Z-methylpropanoic), pivalic (2,2:dimethylpropanoic), Z-methylbutanoic, isovaleric (Ii-methylbutanoic), 2-ethylbutanoic, 2,2-dimethylbutanoic, 2,3-dimethylbutanoic, 3,3 dimethylbutanoic (t butylacetic), isocaproic (4-methylpentanoic), 2,2-dimethylpentanoic, 2,3-dimethylpentanoic, 2-ethyl-2-methylbutanoic, 4,5-dimethylhexanoic, 2-ethylhexanoic, 2,2,4,4-tetramethylpenmoved as desired; thus, the compositions may be prepared in situin liquid hydrocarbon media which may serve as a carrier, e.g. benzene, toluene, heptane, isooctane, diisobutylene, kerosene, gasoline, and mixtures thereof. When a lithium alcoholate is usedas'such or as a concentrated alcoholic solution, the alcohol introduced and formed in the neutralization reaction may or may not be removed, as desired. l 1

The acid-salt compositions themselves at ordinary temperatures may vary from relatively fluid or viscous liquids through semi-solids to solids, depending upon. the chemical structure and physical properties of the particular acids employed in their preparation and upon theacid/salt mol ratio. I

The acid-salt compositions of this invention are adapted to provide practical working" concentrations of dissolved lithium in media consisting essentially of liquid hydrocarbons. The hydrocarbon may constitutethe major component of the solution or a relatively minor component of the solution, such as when they are dissolved in the hydrocarbon fuel itself or when made up as concen trates for addition to fuels either in a hydrocarbon or when the salt is dissolved in the acid itself, as illustrated in the following examples. l

The particular liquid hydrocarbon medium employed in the preparation of concentrates for addition to fuels is not critical. It may be a single hydrocarbon or a mixture of such hydrocarbons such as parafiinic, isoparaffinic, olefinic, naphthenic or aromatic, or blends thereof. The acid-salt mixtures may also be incorporated as concentrates in other gasoline additives such as in the tetraethyllead antiknock compounds. The fuels with which the lithium salts of this invention are to be used are the liquid hydrocarbon fuels which comprise the various gasolines of commerce used in spark-ignition engines. Such fuel may be a clear stock, i.e. not containing additives, or it may be a finished commercial fuel containing additives normally associated with such fuels, e.g. antioxidants, corrosion inhibitors, anti-icing agents, antiknocks, scavenging agents for combustion products of suchantiknocks, etc. a fuel containing an antiknock quantityof tetrae thyllead, e.g. 0.12 to l.5 ml. per liter, and the appropriate quantities of halohydrocarbon scavengers for lead, e.g. ethylene dibromide, ethylene dichloride and the like.

Patented Dec. 19, 1961 By ,the term leaded. fuel as used herein is meant- These acid-salt compositions are effective antiknock agents, and when so employed will be present in quantities providing from about 0.0025 to about 1.5 grams, and preferably 0.05 to 0.5 gram of lithium per liter. By the use of acids, concentrations of lithium as lithium salts in the hydrocarbon solvents even up to about 20 grams per liter have been obtained.

The ratio of acid to salt employed will usually vary depending upon the concentration of the lithium desired in the final fuel. As stated above, the acid/salt ratio will also vary depending upon the chemical structure of the acids and salts used. Usually the acid/salt ratio will be greater as the concentration of such mixture in the hydrocarbon fuel decreases. The acid-salt concentration to be employed in the final fuel mixture will dictate the ratio of the acid-salt mixture in the concentrate made up for addition to fuels.

It has also been found that the presence of small amounts of a lower molecular weight alcohol or other solvent such as dimethylformamide, will substantially lower the amount of acid required to effect complete solution of the lithium carboxylate in the hydrocarbon fuel. The amount of the alcohol or dimethylformamide employed usually will not be more than 0.25 to 1.0 volume percent, based on the hydrocarbon fuel, although larger amounts may be employed if desired. In fuels already containing alcohol or dimethylformamide as a de-icing agent, the ratio of acid to salt may be somewhat lower than that used in a hydrocarbon fuel alone, not containing such agents.

The presence of the acid solubilizing component in the acid-salt compositions of this invention has no deleterious effect on the performance of the liquid hydrocarbon fuels. Usually it exerts the beneficial effect of augmenting the antinock performance of the lithium carboxylate. Further, the acid-salt compositions provide the additional advantage of being markedly more resistant to extraction by water from its hydrocarbon solutions than is the salt itself.

In the examples, the solubilities were determined after centrifuging the solutions at 2700 r.p.m. for minutes to throw out any undissolved material.

The following examples are given to illustrate the invention.

EXAMPLE 1 The solubilizing effect of each of seven branched chain acids was determined by adding 0.1 gram of lithium pivalate to 100 ml. of a commercial aviation gasoline in which the pivalate was substantially insoluble. To the resulting suspension was added approximately an equal molar quantity of the branched chain carboxylic acid, and the mixture was mechanically shaken at room temperatures. After one hour, if a solid phase still remained, the addition of acid was repeated, i.e. a second molar equivalent and then a third, etc., as needed, to effect complete solution of the solid phase. The quantity of each acid required is tabulated below:

obtained in the with commercial approximately 1 Substantially identical results were above gasoline which had been treated tetraethyllead aviation mix to contain ml. of tetraethyllead per liter.

The solutions produced above are stable indefinitely, that is, they remain clear and form no precipitate of lithium salts.

EXAMPLE 2 According to the procedure described in Example 1, approximately 0.1 gram of each of the lithium salts listed below was completely solubilized in 100 ml. of isoctane, by the addition thereof of a carboxylic acid as designated below:

1 In 100 ml. of a loaded (08 ml. tetraethyllead/liter) automotive gasoline.

EXAMPLE 3 Using kerosene in the procedure described in Example 1, 4 grams of 2-ethylhexanoic acid solubilized 1 gram of lithium-Z-ethylhexanoate per liter of kerosene; and using JP-4 jet fuel as the solvent, one gram of the salt was solubilized by 6 grams of the acid per liter of solvent.

EXAMPLE 4 Each of the following lithium carboxylates together with about 3.2 molar proportions of its corresponding carboxylic acid was blended into isoctane by stirring at room temperatures:

2-methyl-2-ethylbutanoate 2,2,4,4-tetramethylpentanoate 3,5 ,5 -trimethylhexanoate 2-ethylhexanoate 2-hexyldecanoate Campholate Isofencholate In each case the quantity of salt was sufficient to provide 0.066 gram of lithium per liter of isooctane. The resulting acid/salt/isoctane compositions were clear liquids.

Substantially identical results are obtained on employing leaded and unleaded commercial automotive and aviation gasolines.

In control tests, in which the carboxylic acid component was excluded, the lithium salts were substantially insoluble.

EXAMPLE 5 A solution of 0.185 gram of Z-methylbutanoic acid in 100 ml. of isoctane was stirred at room temperature with an excess of lithium Z-methylbutanoate (which is normally insoluble) until the solution was saturated with respect to dissolved lithium salt. The isoctane phase contained all of its original acid content and 0.045 gram of lithium 2-methylbutanoate: acid/salt ratio-=4.3:1.

When the above experiment was repeated with isoctane containing 1.85 grams of the Z-methylbutanoic acid, 1.46 grams of the lithium salt dissolved: acid/salt ratio=1.4: 1.

EXAMPLE 6 The procedure of Example 5 was repeated, employing each of the following acids and the corresponding lithium salts thereof, in ml. portions of isoctane:

0.1 gram of 2-hexyldecanoic acid solubilized 0.04 gram of lithium 2-hexyldecanoate; acid/salt ratio=2.5:1; 0.5 gram of 3-methylbutanoic acid solubilized 0.26 gram of its lithium salt; acid/salt ratio=approximately 2:1; 2.0 grams of Z-ethylbutanoic acid solubilized 0.67 gram of its lithium salt; acid/salt ratio=about 3&1; and 26 grams of 3,5,5-trimethylhexanoic acid solubilized 18.2 grams of its lithium salt; acid/ salt ratio -about 1.5 :1.

EXAMPLE 7 Campholic acid, lithium campholate, and the following hydrocarbon solvents were employed in the pro cedure of Example 5. The results are tabulated below:'

EXAMPLE 8 Solution Acid Salt Lithium Acid/salt Molar ratio 1 No isooctane present.

EXAMPLE 9 A mixturev consisting of 30 grams of isofencholic acid and 29 gramsof lithium isofencholate was completely soluble in 100ml. of isooctane at 27 C. In contrast, the solubility of lithium isofencholate, alone in isooctane is less than 0.003 gram per liter.

An equimolar mixture of isofencholic acid and lithium isofencholate, containing 18.2 grams of the salt, was stirred into 100 ml. of isooctane. The resulting solution was diluted with isooctane to /s, then ,4 volume, without the separation of a solid phase occurring.

EXAMPLE 10 2,Z-dimethyloctadecanoate was slurried in isooctane in quantity corresponding to 20 grams of salt and 0.44 gram of lithium per liter, followed by an equal weight, based on the salt, of 2,2-dimethyloctadecanoic acid. The mixture was stirred to produce a clear solution.

In the following examples, the mild knock test was carried out in a Waukesha AST M D909-49T knock test method single cylinder knock rating engine equipped with a four-hole, overhead valve, variable compression ratio head. The engine is mounted on a test stand with a suitable motor-generator unit which absorbs the power output of the engine. A spark plug, mounted in the conventional position for this type engine, a rate of change of pressure pick-up and a steel plug occupy three of the four holes in the head. A Waukesha ASTM D909-49T knock test method fuel injector is inserted into the fourth hole in the head by means of an adapter, and is supplied with fuel from the fuel injection pump. This fuel system 6 injects the fuel directly into the combustion" chamber-.1 With the engine operating, the occurrence of knock'jis determined at the trace knock intensity level by mea'tis of the rate of change of pressure pick-up mounted in the cylinder head. The signal from the pick-up feeds'into a cathode-ray oscilloscope and the occurrence of knock is observed as a shattering of the rate of change of pressure trace on the oscilloscope screen late in the engine cycle. r

The engine is operated under the following conditions:

Test condition mild Speed, r.p m 600 Spark advance (degree before top center) 13 Fuel injection timing (degree after top center on intake stroke) 50 Fuel/air ratio 0.0800- -0.0005 Intake manifold air pressure (in. Hg abs.) ..r 30 Coolant temperature, F 212 Intake temperature, F 200 Oil temperature, F 160 Compression ratio-Varied to produce trade knock.

Under these operating conditions the knock resistance of all fuels tested in this specification is determined by comparing the highest useable knock-free compression ratio of these fuels to that of primary reference fuels consisting of blends of isooctane and'n-heptane below performance number. The knock resistance of all fuels tested is expressed in this specification in terms of Army-Navy Performance Numbers (U.S.A.) as defined in Tables VII and VIII in the ASTM Aviation Method (D614-49T), as recorded in the ASTM Manual of Engine Test Methods for Rating Fuels, published by the American Society for.Testing Materials, October 1952.

This 'testand the test conditions were developed to evaluate antiknock compounds under thesame stresses as would be encountered in automotive operation.

EXAMPLE 1 l A leaded blended gasoline, having a composition-typical of a commercial automotive gasoline and containing 0.8 ml. of tetraethyllead per liter, was treated to contain 0.066 gram of lithium per liter by dissolving in the gasoline a 3:1 molar ratio mixture of 2-ethylhexanoic acid and lithium 2-ethylhexanoate, in quantity providing. 4.5 'grams of the acid and 1.4 grams of the lithium salt per liter of fuel.

As determined in the mild knock test methodythe' performance number of the untreated fuel was.104;' that of the treated fuel was 131.

EXAMPLE 12 A mixture consisting of 1.3 mols of pivalic acid per mol of lithium Z-ethylhexanoate was dissolved, in quantity providing 0.066 gram of lithium per liter, in the gasoline of Example 11. As a result, the performance number of the fuel was raised from 104 to 133 in the mild" test. I

EXAMPLE 13 The gasoline of Example 11 was treated to contain 0.066 gram of lithium per liter by dissolving therein 8.7 grams per liter of a 2.5 :1 molar mixture of 3-hexyldecanoic acid (6.2 grams) and lithium 2-hexyldecanoate (2.5 grams). The performance number of the gasoline was raised thereby from 104 to in the mild test. Only 6% of the lithium salt present in this solution was extracted with 5 ml. of water per 100 ml. of the gasoline solution, while when the same quantity of salt is solubilized in gasoline using 55 g. per liter of ethanol, the same amount of water extracted 96% of the salt from the solution.

EXAMPLE 14 By the use of the blending. agents tabulated below, lithium 3,3-dimethylbutanoate, in quantity providing 1.2 grams per llter of additive (0.066 gram per liter of lith- '7 ium) was dissolved in a super-premium leaded automotive gasoline having a performance number (P.N.) of 105 in the mild test. As a result, the P.N. of the fuel was raised as indicated below:

Blending agent P.N. Increase in IN 40 grams/liter of ethanol 115 10 1.4 grams/liter of pivallc acid 131 26 1.9 grams/liter of Z-ethylhcxanolc acid 129 24 EXAMPLE 15 The previous example was repeated, employing the lithium carboxylates and carboxylic acids tabulated be low. The quantities are in grams per liter, unless otherwise noted.

EXAMPLE 16 A 2:1 molar mixture of pivalic acid and lithium pivalate, in an amount providing 0.05 gram of lithium per liter, was dissolved in a premium unleaded automotive gasoline having a performance number of about 91 in the mild test.

As a result, the performance number of the fuel was raised to 108.

EXAMPLE 17 A 1:1 molar mixture of campholic acid and lithium campholate was dissolved, in amounts provided 0.034 gram and 0.069 gram of lithium per liter of fuel, in a blended gasoline containing 0.8 ml. of tetraethyllead per liter and having a performance number of 116 in the mild test and 86 in the aviation" test, which was carried out by the procedure set forth in ASTM D-909-49T knock test method. As a result, the performance number of the fuel was raised to 126 and 140, respectively, in the mild test and to 98 and 103, respectively, in the avia tion test.

The embodiments of the invention in which an inclusive property or privilege is claimed, are defined as follows:

1. A liquid hydrocarbon fuel for internal combustion engines containing as an antiknock agent a lithium salt of an aliphatic branched chain carboxylic acid, the amount of the lithium salt of the aliphatic branched chain carboxylic acid being increased over its normal solubility in such liquid hydrocarbon by having incorporated therewith an aliphatic branched chain carboxylic acid, the carboxylic acids and the carboxylic acid salts being those in which the carboxy group is attached to a hydrocarbon radical, the molar ratio of acid to salt in the composition being within the range of from about 10:1 to 0.5:1.

2. A liquid hydrocarbon containing dissolved therein at least 0.0025 gram/liter of lithium as a lithium salt of an aliphatic branched chain carboxylic acid in which the solubility of the salt in the liquid hydrocarbon has been effected by incorporating in the hydrocarbon from 0.5 to 10 mols of an aliphatic branched chain carboxylic acid per mol of said salt, the carboxylic acids and the carboxylic acid salts being those in which the carboxy group is attached to a hydrocarbon radical.

3. A method for improving the solubility of lithium salts of aliphatic branched chain carboxylic acids in liquid hydrocarbons, which comprises incorporating in the hydrocarbon solution from 0.5 to 10.0 mols of an aliphatic branched chain carboxylic acid per mol of salt present, the carboxylic acids and the carboxylic acid salts being those in which the carboxy group is attached to a hydrocarbon radical.

References Cited in the file of this patent UNITED STATES PATENTS 1,692,784 Orelup et al Nov. 20, 1928 2,151,432 Lyons et al Mar. 21, 1939 2,280,474 Byrkit et al Apr. 21, 1942 2,616,905 Assetf et a1 Nov. 4, 1952 2,751,283 Van Strien et al. June 19, 1956 2,935,973 Sandy et al May 10, 1960 2,935,974 Sandy et a1 May 10, 1960 2,935,975 Sandy et a1 May 10, 1960 FOREIGN PATENTS 1,011,549 Germany July 4, 1957 300,156 Great Britain Nov. 6, 1928 312,245 Great Britain May 17, 1929 640,311 France Mar. 26, 1928 658,059 France Jan. 22, 1929 

1. A LIQUID HYDROCARBON FUEL FOR INTERNAL COMBUSTION ENGINES CONTAINING AS AN ANTIKNOCK AGENT A LITHIUM SALT OF AN ALIPHATIC BRANCHED CHAIN CARBOXYLIC ACID, THE AMOUNT OF THE LITHIUM SALT OF THE ALIPHATIC BRANCHED CHAIN CARBOXYLIC ACID BEING INCREASED OVER ITS NORMAL SOLUBILITY IN SUCH LIQUID HYDROCARBON BY HAVING INCORPORATED THEREWITH AN ALIPHATIC BRANCHED CHAIN CARBOXYLIC ACID, THE CARBOXYLIC ACIDS AND THE CARBOXYLIC ACID SALTS BEING THOSE IN WHICH THE CARBOXY GROUP IS ATTACHED TO A HYDROCARBON RADICAL, THE MOLAR RATIO OF ACID TO SALT IN THE COMPOSITION BEING WITHIN THE RANGE OF FROM ABOUT 10:1 TO 0.5:1. 